The present invention relates to the field of ophthalmic instruments, and more particularly, to an improved, stereoscopic vision tester designed for rapid and precise measurement of visual performance, speed and ease of operation, and convenience of maintenance. The present invention is designed to provide a wide variety of standard vision tests in a small, compact, light-weight, portable instrument.
Eye testing devices are well-known for use in conducting limited testing of ophthalmic abilities of individuals. Such devices are particularly well suited for administering driver's license vision tests, mass screening of job applicants, and periodic vision testing of students. Devices of this type are described, for example, in such patents as U.S. Pat. No. 3,012,472 to Feinberg et al, U.S. Pat. No. 4,452,515 to Lewis, U.S. Pat. No. 4,027,954 to Good, U.S. Pat. No. 2,364,793 to Jobe et al, U.S. Pat. No. 2,798,408 to Ellis et al, and U.S. Pat. No. 3,205,505 to Fletcher et al.
The patent to Feinberg et al may be taken as representative of the types of devices presently available in the market. The eye testing apparatus according to Feinberg includes a light-occluding casing with a viewing device coupled thereto. The viewing device includes a headpiece and left and right lenses. Inside the light-occluding casing is a rotatable drum which holds a plurality of test slides on the drum surface. The drum is rotated by a handle extending through the side of the casing, and different test slides are thus presented to the person looking through the viewing device. The test operator rotates the drum, questions the test subject on the test slides he/she observes, and then manually records the test result.
The Feinberg device is also capable of testing near vision (approximately 14 inches) and far vision (approximately 20 feet). Within the drum are located four light bulbs. A first pair of light bulbs is positioned to illuminate a near test slide, while a second pair of bulbs is positioned to illuminate a far test slide. Each pair of bulbs includes a left and a right bulb. Within the viewing device is located a viewing frame which is angularly adjustable to alternately provide vision of the near test slide and the far test slide. The viewing frame is angled downward to view the near test slide in a direct optical path. The viewing frame is angled upward to view the far test slide after reflection of the test slide image from an optical mirror inside the casing. This reflection of the image increases the optical distance between the test subject and the far test slide to approximate far vision. Thus, the near/far test apparatus is complicated, bulky, requires four individual light bulbs, and a mirror which must be accurately positioned and kept clean.
Other near/far testing devices are known which include bifocal lenses inserted in the viewing device. Shutters are then manipulated to block either the top or the bottom of the bifocal lenses to switch between near and far vision. Such devices suffer from the same disadvantages of the Feinberg device.
Another disadvantage of the Feinberg device is the difficult maintenance required to change any of the light bulbs. The rotatable drum of Feinberg is coupled to the casing at both ends of the drum. Thus, to change a light bulb the apparatus must be disassembled and the drum must be removed from the casing. Therefore, replacing a light bulb requires a skilled maintenance technician and consumes a great deal of time. But, typically a vision tester of this sort is designed to be operated by relatively unskilled operators. Additionally, while handling the drum the test slides may become broken and/or marred, thus reducing vision test accuracy. Furthermore, to change a test slide on the rotating drum, the apparatus must again be disassembled further increasing maintenance cost and time.
Yet another disadvantage of the Feinberg device is the difficulty the test operator experiences in attempting to ascertain which test slide the test subject is observing. The device of Feinberg includes a viewing port cut into the side of the casing which allows a test operator to peer inside the machine to observe the same test slide as the test subject. Other known devices also include such ports cut into the casing at various locations to allow the test operator to confirm which test slide is being viewed by the subject. All such ports cut into the casing permit light to enter, thus obscuring the vision of the test subject. Such ports also may allow the entry of foreign materials which can cloud the test slides and degrade the performance of the moving parts.
A further disadvantage of devices such as Feinberg is the necessity for the test operator to position himself/herself immediately adjacent the testing device. The test operator must manually rotate the test drum and frequently peer through the vision ports to confirm the observed test slide. This is disadvantageous in that the test subject may be made uneasy by the immediate presence of the test administrator. A vision tester which allows the test administrator to sit at a comfortable distance from the machine and the test subject would be very beneficial in aiding the accuracy of the test results.
Finally, such devices as Feinberg contain no means for testing horizontal visual field (peripheral vision). It is recognized that peripheral vision tests are very important to vision accuracy for driving and proper job performance. There are devices on the market which provide for peripheral vision testing by implanting a series of light emitting diodes (LEDs) in the headrest immediately adjacent the left and right viewing lenses. The LEDs are positioned at various angles with respect to the eye of the test subject. The LEDs are then selectively illuminated to determine the horizontal visual field of the test subject. A disadvantage of such known devices is that the implanted LEDs are very difficult to replace or service. Again, the eye testing apparatus must be disassembled and the LEDs must be removed from the very small space inside the headrest of the viewing device. An additional disadvantage of such known peripheral testing devices is that they may be easily circumvented by the test subject. Thus, the test subject can merely move away from the viewing lenses to more easily observe the LEDs implanted in the headrest. Thus, a test subject may have defective horizontal visual field yet still provide correct answers to the test operator.
With the rapid proliferation of computers in schools and offices, an increasing number of people are required to spend significant amounts of time operating computer terminals and observing a cathode ray tube. Such visual display terminal operators typically position themselves between 20 and 40 inches from the CRT. Since standard vision tests measure only near and far vision, vision problems occurring between 20 and 40 inches may disable some people from accurately operating a visual display terminal. Thus, it would be beneficial if vision testing devices could test the intermediate range of vision of each test subject. No known devices are capable of testing such intermediate vision.
Finally, no known devices are capable of being interfaced with a computer. Such a computer interface would be very beneficial to store the massive amounts of data inherent in a mass vision screening system. Thus, driver's license testing stations could interface each testing device to a computer which would store vision test records of each driver's license recipient. A few known vision testing devices include a computer as part of the apparatus. This computer aids in performing the test and provides a print-out of the test results. However, none of these known devices have a provision for optionally interfacing the vision test apparatus with any number of computers. Such a vision test apparatus could be accomplished by including a RS-232 interface in the vision testing device. Then, the vision tester could be interfaced with a wide variety of professional and personal computers.
Thus, from the above discussion, it is apparent that advances in technology and improved design could provide a vision testing device which is compact, provides accurate test results, allows convenient test administration, and is easy to maintain.